This invention relates to a method for producing aluminum-base alloy substrates for magnetic recording media such as magnetic memory discs, and more particularly to a method for producing aluminum-base alloy substrates for magnetic discs, which have few surface defects and excellent surface uniformity after grinding or polishing.
The magnetic discs which are most widely used as a memory medium for computers are generally produced by machining a substrate of an aluminum alloy to a predetermined thickness followed by precision grinding and coating of the surface of the substrate with a thin film of a material which is magnetizable for recording signals. The magnetic disc substrate of this sort is required to meet the following conditions.
(1) The surface roughness after precision polishing should be small enough to maintain a constant flying height of the magnetic head for stable read/write characteristics.
(2) On polished substrate the surface defects which adversely affect the uniform formation of the coated film of the magnetizable material should be few and of sufficiently small dimensions.
(3) The substrate should have sufficient mechanical strength to withstand machining and grinding in the fabrication process as well as highspeed rotation while in the softened state.
(4) The substrate should have good corrosion resistance and a certain degree of heat resistance.
(5) It should be non-magnetic, light in weight and low in cost.
The magnetic disc substrates which are currently most popular in the art are made of an aluminum alloy AA 5086. However, recently there has been an increasing demand for magnetic discs having a large capacity and high density. It is necessary to obtain such high density disc that magnetic area for each bit of signal, thickness of magnetic film and flying height of the head should be reduced. Consequently, the finished surface of substrate have excellent uniformity to provide such high density disc. In this regard, the abovementioned alloy AA5086 is unsatisfactory in surface uniformity.